(57) A system for coding of digital video images such as bi-directionally predicted video
object planes (B-VOPs) (420), in particular, where the B-VOP and/or a reference image
(400,440) used to code the B-VOP is interlaced coded. For a B-VOP macroblock (420)
which is co-sited with a field predicted macroblock of a future anchor picture (440),
direct mode prediction is made by calculating four field motion vectors (MVf,top, MVf,bot, MVb,top, MVb,bot), then generating the prediction macroblock. The four field motion vectors and their
reference fields are determined from (1) an offset term (MVD)of the current macroblock's coding vector, (2) the two future anchor picture field
motion vectors (MVtop, MVbot), (3) the reference field (405,410) used by the two field motion vectors of the co-sited
future anchor macroblock, and (4) the temporal spacing (TRb,top, TRb,bot, TRD,top, TRD,bot), in field periods, between the current B-VOP fields and the anchor fields. Additionally,
a coding mode decision process for the current MB selects a forward, backward, or
average field coding mode according to a minimum sum of absolute differences (SAD)
error which is obtained over the top (430) and bottom (425) fields of the current
MB (420).
|
|
